Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $73.49   11.763%   $82.1346   $82.13   $82.15   $82.10  
  Purchase #2 $245.44   4.610%   $256.7548   $256.75   $256.75   $256.80  
  Purchase #3 $113.38   7.858%   $122.2894   $122.29   $122.30   $122.30  
  Purchase #4 $239.39   9.137%   $261.2631   $261.26   $261.25   $261.30  
  Purchase #5 $41.96   11.498%   $46.7846   $46.78   $46.80   $46.80  
  Purchase #6 $147.72   3.629%   $153.0808   $153.08   $153.10   $153.10  
  Purchase #7 $100.81   9.323%   $110.2085   $110.21   $110.20   $110.20  
  7 purchase totals = $962.19       $1,032.5158   $1,032.50   $1,032.55   $1,032.60